This invention relates generally to commutatorless electrical motors, and more particularly, the present invention relates to structure of a magnetic rotor of such a motor having rotational position detecting elements.
In conventional commutatorless electrical motors, Hall generators are provided for detecting the position of the rotor so that currents respectively flowing through armature windings disposed on the stator are changed over. The output voltages from the Hall generators are fed to a switching circuit in which energization of the armature windings is effected in a sequence. However, the voltages from the Hall generators are not uniform and therefore, it is difficult to provide accurate switching timing. Furthermore, since the output voltage from Hall generators is relatively low because the magnetic flux density around the end of cylindrical magnetic rotor is lower than that in the vicinity of the inner surface of the cylinder. Low voltages from Hall generators result in slow switching of the armature currents, and thus armature winding current flowing angle corresponding to energization time length is apt to be widened, deteriorating the efficiency of the electrical motor. Namely, in conventional commutatorless electrical motors, torque ripple, i.e. variation in rotational torque, occurs due to error in rotational position detection. In order to compensate for the above defects of commutatorless electrical motors having Hall generators as rotational position detecting elements, input currents of the Hall generators have been increased in some conventional motors. However, such a conventional commutatorless electrical motors have suffered from a problem that current consumed by the Hall generator is very large.